1. Field of the Invention
This invention relates to bearing lubrication systems and, in particular, to lubrication systems having a pressurized oil reservoir, an emergency gas system for backup flow capability, and a means for controlling the emergency gas system and the lubricant level at the gas fluid interface of such a system.
2. Description of the Prior Art
As is well known, large rotating apparatus, such as a turbine, have a rotor member extending centrally and axially therethrough and at each axial end of the rotor at a point exterior to the casing is provided a suitable bearing to rotatably support the rotor member. In order to assure that the bearings properly perform this function, it is of primary importance that they be supplied with a suitable lubricating fluid. For this purpose, the prior art has disclosed elaborate bearing lubricating fluid systems to supply the necessary lubricant to the bearings.
At present, there are several methods known to the art among which is a steam turbine lubricating system utilizing an oil pump mounted on the turbine rotor shaft as a device to provide lubricating oil under pressure to the turbine bearings. This shaft-mounted oil pump uses the kinetic energy of the rotor to provide an energy source independent of other interruptible power sources to convey fluid to the bearings. The shaft-mounted main oil pump provides motive oil to an oil ejector, which is located within a lubricating fluid reservoir. The discharge of the ejector supplies lubricating fluid under pressure to an oil cooler and then to the turbine bearings. A portion of the pressurized fluid at the discharge of the ejector is also supplied to the shaft-mounted pump suction to prime the shaft-mounted pump, i.e., to maintain a supply of fluid thereto.
After serving its lubricating system purpose within the bearing member, oil returns to the reservoir by gravity through a suitably disposed oil strainer. The reservoir itself is located a significant distance beneath the centerline of the turbine apparatus. All of the oil supply lines emanating from the reservoir to the bearings are surrounded by a guard pipe to insure that any leak developed within the fluid lines will drain to the oil reservoir. As a condition to this safety requirement, it is apparent that the reservoir itself must be of sufficient size to hold all the runback of oil of the entire system. Motor driven pumps are mounted on the reservoir and provide oil to the turbine bearing during those periods when the rotor is moving up to or coming down from rated speed.
Any oil lubricating system, the above-described being typical of a prior art embodiment, must meet three reliability conditions. A lubricating system must, first, provide oil to the bearing with minimal possibility of any interruption of oil supply; second, provide oil at a temperature cool enough to be utilized by the bearings; and, third, provide oil to the bearings that is not contaminated by foreign matter. In addition to the reliability conditions just outlined, it is desirable that a lubricating system be efficient so as not to overly detract from the efficiency of the entire power plant. With these requirements in mind, it is apparent that the prior art systems, although meeting the reliability requirements, do so at a cost to the overall efficiency of the power plant.
For example, although the prior art system is reliable, since the use of three pumps each powered by an independent power source reduces the probability that flow to the bearings will be interrupted, considerable power from the shaft-mounted pump is required in order to provide the necessary motive power to lift the lubricating fluid from the reservoir to the turbine bearings and also to the shaft-mounted pump suction. On a typical nuclear unit of 1200 mw, for example, such a turbine shaft-mounted pump requires 800 kw in order to provide motive oil for the lubrication functions. This reduces the overall efficiency of the turbine by 0.07%. As a further disadvantage, if the system utilizes an ejector to establish pressure of the oil flowing to the bearings, a limited discharge pressure is available due to the very nature of the ejector apparatus. Therefore, there is a limited range of distances that the reservoir may be located from the turbine, thus reducing overall power plant flexibility. Further, the motor driven pumps mounted on the reservoir may themselves require 75 to 100 horsepower to provide fluid to the bearings when they are called upon to do so.
A still further disadvantage in the prior art systems is the high temperature at which fluid is stored in the reservoir. The prior art maintains fluid in the reservoir at the drain temperature of approximately 150.degree. F. In the event of loss of cooling water to the oil coolers located downstream of the reservoir, there is a possibility of damage to the bearings due to the introduction thereinto of hot oil. Also, the physical size of the conduits required by prior art systems occupies a greater portion of power plant area, this directly increases the cost of these facilities.
There is another disadvantage that is very evident in the case of turbines. For each turbine there also must be a new shaft mounted pump manufactured. The system as disclosed by this invention reduces engineering and mnaufacturing cost by utilizing commercially available motors and pumps, thus reducing the need for engineering, precision machining and other manufacturing cost.
It is apparent that an improved lubricating fluid system for the bearing of a turbine apparatus which eliminates these aforementioned problems of the prior art is desired.
In U.S. Pat. No. 4,002,224 an improved lubricating system was disclosed. This lubricating system comprises a lubricating fluid reservoir having therein a pressurized storage section and a nonpressurized drain section. Suitable pumping means, such as an electrically driven pump, is mounted on the reservoir and pumps fluid from the non-pressurized drain section, through an oil cooler, and into the pressurized section and to the bearings. Fluid discharged from the bearings is collected in the non-pressurized drain section and provides fluid to satisfy the pump suction. Provision of the oil cooler immediately upstream of the pressurized section maintains oil in storage at a cooler temperature than in the prior art.
An emergency backup system is provided to maintain bearing oil flow in the event of a system malfunction. The emergency system utilizes an external pressurized gas supply and provides pressure to maintain lubricant flow upon activation by a suitable mechanical control arrangement. In this embodiment, the gas and lubricating fluid are maintained isolated along a fluid gas interface within a separate section within the reservoir.
The prior art also discloses means for providing lubricant in the event the main pump means should be inoperative such as during deceleration. For example, in U.S. Pat. No. 3,147,821 a system was disclosed which utilized either compressed gas or gravity to provide lubricant in decreasing amounts during the deceleration period.
In United Kingdom Pat. No. 1,167,602, there is a backup hydraulic accumulator through which compressed gas forces lubricant to the bearings after detection of loss of pump pressure by means of a spring bias switch.